Synthesis and characterization of thieno[3,4-b]pyrazine-based low band gap materials: Monomers, oligomers, and polymers.

Conjugated organic polymers have become one of the major focuses of materials chemists, and have attracted considerable fundamental and technological attention due to their tunable optical and electronic properties. Because of their environmental stability and good tunability, polymeric and oligomeric thiophenes and their derivatives have been widely applied to light-emitting diodes, field-effect transistors, photodetectors, and photovoltaic cells. One such system, poly(thieno[3,4-b]pyrazine)s, showed as promising materials for optoelectronic applications. The synthesis of thieno[3,4-b]pyrazines (TPs), however, was limited because of the low yield of one important precursor, 2,5-dibromo-3,4-dinitrothiophene. A new nitration protocol for this precursor has been developed, giving the reaction essentially quantitative yield. In addition, a series of new functionalized TPs has been produced, which significantly enhanced the tunability of TPs and expanded the TP family. It has been found that extending the conjugation of TPs enhances both optical and electronic properties. A variety of TP-based oligomers have been synthesized and characterized. The results showed that the more TP components there were in the oligomers, the lower the HOMO-LUMO energy gaps of these oligomers were. In order to produce processable TP polymers, the GRIM method has been applied to produce these materials. Polymers produced by this method exhibited better solubility, processibility, and film formation.